A fan-based term for a sprite or sprite edit made by using parts of more than one pre-existing sprite.

(click to see full-sized version)

Frankensprites have different uses, including adding new animation frames to old characters and making new characters by splicing two parts from two different characters together. The term is usually used to describe fan-made sprites, this is done in professional games, often through using alternate heads (head swaps) or other outfit parts though tile swapping.

The tutorial in this link was made a loooooooong time ago, showing steps based on how I frankensprited back when I mostly made sprite edits.